Conventionally, means for securing a closure on a container are formed in part on the closure and in remaining cooperating part on the container. Thus a closure may have inside threads that cooperate with outside threads on the finish of a container; or a closure may have lugs that cooperate with lugs or seats on a container; or a closure may have a bead designed to snap over a rib on a container. The need to form part of the securing means on the container usually increases mold or die cost as well as the amount of material required for the container. Further, the provision of securing means on a container limits that container to use with a particular type of closure, and vice versa.
Moreover, where the closure is of the twist-on, twist-off type, the commercial filling process is slowed by the need to twist the closures onto the containers. Press-on closures, that is, closures which are applied by downward press-on force rather than twisted on, can be applied much more quickly on a filling line than twist-on closures, but they do not generally provide as secure a seal. Press-on, pry-off closures also require more force for removal than twist-off closures, and once removed they do not reseal as effectively as twist-off closures.
Metal containers, for example, cans, are often formed without any threads or other securing means, as the result of which a screw-on closure, indeed any closure that will tightly reseal, cannot be applied to such containers.